In this work, thermal degradation of polyurethanes containing different feed concentration of 4- [bis(2-hydroxyethyl)amino]-4'-nitroazobenzene as nonlinear optical chromophore (NLO) is presented, using dynamic thermogravimetric analyzer (TGA) in air atmosphere at different heating rates viz. 5, 10 and 20°C min-1. Polyurethanes were synthesized by copolymerization of 4-[bis(2-hydroxyethyl)amino]-4'-nitroazobenzene and N-phenyldiethanolamine with 2,4- tolyenediisocyanate. Degradation activation energies are calculated using model free multipleheating rate methods i.e. Kissinger, Friedman and Ozawa-Flynn-Wall. The values of activation energy thus obtained are directly proportional to the feed concentration of chromophore.The lower value of activation energy for polyurethane containing 100% chromophore feed concentration suggests its lower resistance to heat during its use in electro optic device applications.